Groundwater is the water that soaks into the ground from rain and can be stored beneath the ground. An aquifer is a body of rock and/or sediment that holds groundwater. There are two main types of aquifer in Ireland: bedrock aquifers and sand and gravel aquifers. Bedrock aquifers are found in cracked bedrock and in limestone bedrock which has been partly dissolved to create cavities.

Bedrock is the solid rock at or below the land surface. Over much of Ireland, the bedrock is covered by materials such as sands and gravel. The sands and gravels occur naturally on top of the bedrock. They were laid down by meltwater from melting ice sheets, by rivers, or by wind.

There are two main types of bedrock aquifer. In most of them, groundwater flows through fractures and fissures. In about half of the limestone rocks, groundwater flows through cavities and caves. This type of limestone is called karst.

The bedrock aquifer map shows the potential of areas in Ireland to provide water supplies. There are three main groups based on their resource potential:

• Regionally important – the aquifers are capable of supporting large public water supplies sufficient to support a large town;

• Locally important – the aquifers are capable of supporting smaller public water supplies or group schemes;

• Poor – the aquifers are only capable of supporting small supplies, such as houses or farms, or small group schemes.

The three main groups are broken down into seven bedrock aquifer categories in total. Please read the lineage for further details.

Information used to assign bedrock aquifer categories include: rock type (Hydrostratigraphic Rock Unit Groups - simplified bedrock geology with similar hydrogeological properties), yield (existing wells and springs), permeability and structural characteristics. All of the information is interpreted by a hydrogeologist and areas are drawn on a map to show the aquifers.

This Bedrock Aquifer map is to the scale 1:100,000 (1 cm on the map relates to a distance of 1km).

It is a vector dataset. Vector data portray the world using points, lines, and polygons (areas).

The aquifer data is shown as polygons. Each polygon holds information on the aquifer code, description, rock unit name, rock unit description, Hydrostratigraphic Rock Unit Group Name, Hydrostratigraphic Rock Unit Group Changes, Bedrock Geology 100k newcode, stratigraphy code (rock layers with age profile), lithology code (rock type), Original Aquifer Category and Comments.